1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a sheet, such as a copying machine, a printer or a facsimile apparatus.
2. Related Background Art
In the field of image forming apparatus such as a copying machine, a printer or a facsimile apparatus, there have been proposed various configurations on the arrangement of a sheet cassette or a sheet tray for containing and supporting sheets for image formation, image forming means for forming an image on a sheet, fixing means for semi-permanently fixing an image transferred onto a sheet, and control means for controlling the operation of the apparatus and the image forming process. The following explanation will be given on a laser beam printer (hereinafter simply represented as printer) as an example.
The principal configuration of a conventional printer is shown in FIGS. 4 and 5.
A printer, constituting an image forming apparatus, is provided with a sheet supplying portion, including a sheet cassette 101 serving as sheet supporting means for supporting and containing sheets for image formation, and sheet supplying means 102 for feeding the sheet supported by the sheet cassette.
Also an image forming portion is composed of a process cartridge 103 integrally formed of a photosensitive drum 104 for image formation, a charger for uniformly charging the photosensitive drum, a developing device for forming a toner image on the photosensitive drum and a toner container, and a laser scanner 105 for writing image information by a light beam onto the photosensitive drum charged by the charger.
In a position opposed to the photosensitive drum across the conveying path of the sheet, there is provided a transfer charger 106 constituting transfer means for transferring the toner image, formed on the photosensitive drum, onto a sheet. Also in a downstream position of the transfer means, there are provided paired fixing rollers 107 serving as fixing means for semi-permanently fixing the toner image transferred onto the sheet, and the sheet on which the image is fixed by the paired fixing rollers is thereafter discharged onto a sheet discharge tray 108 provided outside the apparatus.
Such sequence of image forming operations onto the sheet is more or less same in any printer, but the features of the printer vary according to the arrangement of the sheet conveying path within the apparatus.
In the printer shown in FIG. 4, the above-described sheet conveying path is provided approximately horizontally in the apparatus. In FIG. 4, a sheet cassette 101 is provided in an inclined position, with respect to the horizontal plane, at the right-hand end portion of the apparatus, and sheet supplying means 102 is provided at an end portion of the sheet cassette. The sheet conveying plane is provided substantially horizontally toward paired fixing rollers 107, while image forming means such as a process cartridge 103 is provided above the conveying path and a transfer charger 106 is provided in an position opposed thereto. The sheet bearing the transferred image is discharged onto a sheet discharge tray 108 positioned approximately parallel to the sheet cassette 101.
Also a printer shown in FIG. 5 has a configuration obtained by rotating, by 90xc2x0, the image forming apparatus shown in FIG. 4. More specifically, in this type of the apparatus, the sheet cassette 101 and the sheet discharge tray 108 are provided substantially horizontally, and a sheet fed by the sheet supplying means 102 from the sheet cassette 101 at the lowermost part of the apparatus is conveyed in a substantially vertical direction, with respect to the horizontal plane, for performing image forming and fixing operations.
As explained in the foregoing, the sheet conveying path in the recent printers is often formed linearly and substantially horizontally or vertically from the sheet supply means 102 to the fixing means 107, and, in such configuration, the position of the fixing means 107 becomes a problem.
The fixing means 107 achieves fixation of the toner onto the sheet by fusing the toner deposited on the sheet, by heat generated by heating of the fixing roller and by a pressure generated at the nip of the paired rollers. Consequently the fixing means 107 generates a large amount of heat at the image formation, thereby elevating the temperature in the apparatus.
In the image forming apparatus of a type in which the sheet is conveyed substantially horizontally as shown in FIG. 4, the process cartridge 103 and the laser scanner 105 are positioned at the side of and above the fixing means 107 constituting the source of heat, so that the heat generated by the fixing means 107 may result in inconveniences such as fusion and solidification of the toner contained in the process cartridge 103 or a change in the refractive index of optical lenses provided in the laser scanner 105.
Also circuit boards of the control means 109, such as an electric supply portion or a driving portion for controlling the apparatus are to be provided in a space available substantially parallel to the sheet conveying path. Since such electric supply portion and driving portion also generate heat, there is required, in order that the process cartridge 103 and the laser scanner 105 are not affected by such generated heat, means for preventing the temperature increase in the apparatus as well as for dissipating the heat generated by the fixing means 107. This has been achieved by providing a plurality of heat insulating members for preventing the temperature increase in the apparatus or providing a fan for air cooling the interior of the apparatus, but such means results in an increase in the cost and dimension of the apparatus.
Also in the sheet supplying operation, the leading end of a sheet fed by the sheet supply means 102 reaches the image forming portion so that the image forming operation is started, before the trailing end of the sheet comes out of the sheet supply means 102. Therefore, when the trailing end of the sheet comes out of the sheet supply means 102, a vibration is generated in the sheet by a large diversion in the direction thereof, and such vibration is transmitted to the image forming portion to perturb the image formed on the sheet.
Also in the apparatus of a type in which the sheet is conveyed substantially vertically as shown in FIG. 5, the process cartridge 103 and the laser scanner 105 are relieved from the influence of heat since the fixing means 107 is provided in the uppermost position of the apparatus, but a higher precision is required for such conveying control and image forming operation because the sheet is conveyed substantially vertically against the force of gravity. Such higher precision has been achieved by providing sheet conveying guide members and paired conveying rollers in a number larger than in the apparatus in which the sheet is conveyed horizontally, but such measure results in an increase in cost and dimension of the apparatus.
Also the mounting angle of the laser scanner becomes larger than in the horizontally conveying type (cf. FIG. 4) to result in a larger load on the bearing of a scanner motor, whereby the bearing becomes deteriorated sooner to shorten the service life of the apparatus.
Also a large diversion in the direction of the sheet, as in the case of the type shown in FIG. 4, results in drawbacks such as vibration noise and a perturbation in the image.
In order to resolve the above-mentioned drawbacks, the apparatus has been so designed as to increase the dimension of the entire apparatus thereby separating the heat-generating fixing means from components susceptible to heat or as to adopt a layout allowing horizontal positioning of the laser scanner, but such measure does not lead to fundamental resolution of these drawbacks but results in other drawbacks such as an increase in dimension or manufacturing cost of the apparatus.
In consideration of the foregoing, an object of the present invention is to provide a compact image forming apparatus.
Another object of the present invention is to provide an image forming apparatus lighter in weight.
Still another object of the present invention is to provide an image forming apparatus excellent in sheet conveying ability.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supply means;
image forming means for forming an image on a sheet fed by the sheet supply means;
fixing means for fixing the image formed on the sheet;
a sheet guide for guiding the movement of the sheet; and
a control board bearing an element for controlling the image forming means;
wherein the sheet guide provided between the sheet supply means and the fixing means is positioned substantially linearly in such a manner that the sheet moves upward in an inclined direction, and the control board is provided in a space under the sheet guide and at the bottom face of the apparatus.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supply means;
image forming means for forming an image on a sheet fed by the sheet supply means;
fixing means for fixing the image formed on the sheet;
a sheet guide for guiding the movement of the sheet; and
a drive source for driving the sheet supply means and the fixing means;
wherein the sheet guide provided between the sheet supply means and the fixing means is positioned substantially linearly in such a manner that the sheet moves upward in an inclined direction, and the drive source is provided in a space under the sheet guide.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supply means;
image forming means for forming an image on a sheet fed by the sheet supply means;
fixing means for fixing the image formed on the sheet, the fixing means being positioned in an upper part of the apparatus;
an air path for introducing the external air from a lower part of the apparatus and generating an air flow utilizing the heat generated by the fixing means; and
an exhaust aperture for discharging the air flowing in the air path to the exterior of the apparatus.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supply means;
image forming means for forming an image on a sheet fed by the sheet supply means;
fixing means for fixing the image formed on the sheet;
a sheet guide for guiding the movement of the sheet, the sheet guide being provided between the sheet supply means and the fixing means and being so positioned substantially linearly that the sheet moves upward in an inclined direction;
an electric supply portion including a power source for supplying the main body of the apparatus with an electric power, the electric supply portion being provided in a lower part of a space formed under the sheet guide;
an air path for introducing the external air from a lower part of the apparatus and generating an air flow utilizing the heat generated by the fixing means; and
an exhaust aperture for discharging the air flowing in the air path to the exterior of the apparatus.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supply means;
image forming means for forming an image on a sheet fed by the sheet supply means;
fixing means for fixing the image formed on the sheet;
a sheet guide for guiding the movement of the sheet, the sheet guide being provided between the sheet supply means and the fixing means and being so positioned substantially linearly that the sheet moves upward in an inclined direction;
a first air path for introducing the external air from a lower part of the apparatus and generating an air flow utilizing the heat generated by the fixing means; and
a first exhaust aperture for discharging the air flowing in the first air path to the exterior of the apparatus;
a second air path for introducing the external air from a lower part of the apparatus and generating an air flow utilizing the heat generated by an electric supply portion provided in a lower part of a space formed under the sheet guide; and
a second exhaust aperture for discharging the air flowing in the second air path to the exterior of the apparatus.
Still another object of the present invention is to provide an image forming apparatus comprising:
sheet supporting means for supporting sheets;
sheet supply means for supplying the sheet from the sheet supporting means;
image forming means for forming an image on the sheet;
fixing means for fixing the image formed on the sheet;
wherein a sheet conveying path from the sheet supply means to the fixing means is substantially linear and substantially parallel to the diagonal of a frame supporting the sheet conveying path.
Still another object of the present invention is to provide an image forming apparatus comprising:
a base frame including two side plates provided perpendicularly to an installation plane of the apparatus, a plate-shaped first stay mounted to the two side plates and positioned at the bottom side of the side plates, a plate-shaped second stay mounted to the two side plates and positioned in an upper side of the apparatus, and a plate-shaped third stay positioned between the first and second stays;
wherein the first, second and third stays are provided in a substantial Z-shape between the two side plate.
Still other objects of the present invention will become fully apparent from the following detailed description which is to be taken in conjunction with the accompanying drawings.